1. Field of the Invention
The invention relates to novel fluid compositions for use in an electrophoretic display device, electrophoretic display devices containing such display fluids, and methods of displaying images with the electrophoretic display devices.
2. Description of Related Art
Electrophoretic displays, also more commonly referred to as electronic paper, are well known in the art. An electrophoretic display generally comprises a suspension of a single type of charged pigment particles colloidally dispersed in a colored liquid of matching specific gravity contained in a cell comprising two parallel and transparent conducting electrode panels. The charged particles are transported between the electrode panels under the influence of an electric field, and can therefore be made to display an image through appropriate application of the electric field on the electrodes. The advantages of electrophoretic displays as a means for providing information and displaying images has been well appreciated in the prior art.
U.S. Pat. No. 4,272,596, incorporated herein by reference in its entirety, illustrates a typical electrophoretic display structure. The electrophoretic display device comprises a pair of electrodes associated so as to form a cavity therebetween, which cavity is filled with an electrophoretic suspension layer comprising a colored suspending medium containing colloidal sized particles in an electrically insulating liquid and finely divided electrophoretic particles suspended in the suspending medium. A source of electrical potential is coupled to the electrodes and with an electric field applied, the marking particles form an image as they follow the field. See especially FIG. 1 therein.
U.S. Pat. No. 6,113,810 describes a dielectric dispersion for use in an electrophoretic display that includes a dielectric fluid, a first plurality of particles of a first color having a surface charge of a selected polarity dispersed within the dielectric fluid and a second plurality of particles of a second color having a surface charge of opposite polarity to that of the first plurality and a steric repulsion thereto preventing coagulation of the first and second pluralities. In one embodiment, the first and second plurality of particles are each formed by separate two stage dispersion polymerization reactions. Each set of particles is formed with unique secondary and functional monomers. Corresponding charge control agents are added to the dispersion to establish opposite polarities on the respective particles.
U.S. Pat. No. 6,017,584 discloses encapsulated displays, i.e., displays in which the electrophoretic fluid is encapsulated within a microcapsule. This fluid may be a mixture of two or more fluids or may be a single fluid. The displays may further comprise particles dispersed in a suspending fluid, wherein the particles contain a liquid. In either case, the suspending fluid may have a density or refractive index substantially matched to that of the particles dispersed therein. Application of electric fields to any of the electrophoretic displays described therein is indicated to affect an optical property of the display.
While improvements have been made in the field of electrophoretic displays, many problems still need to be addressed in order for electronic paper applications to move toward large commercial scale production and use. For example, quality and resolution of the display devices can continue to be further improved.
It is thus an object of the present invention to develop novel electrophoretic display fluids that are improved in operation and exhibit improved image quality and resolution when used in an electrophoretic display device.
It is a still further object of the present invention to develop improved methods of operating an electrophoretic display device to obtain higher quality and higher resolution images.
These and other objects are achieved by the present invention, which in embodiments is directed to a method of displaying an image with an electrophoretic display device, the electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, and wherein the electrophoretic display fluid comprises a first set of particles and a second set of particles each dispersed in a transparent liquid system, the first set of particles exhibiting a color different from and contrasting to a color of the second set of particles, and wherein the first set of particles are magnetic particles while the second set of particles are non-magnetic particles, the method comprising appropriately applying an electric field and a magnetic force to a selected individual reservoir in a manner to cause either the first set of particles or the second set of particles to be displayed.
In embodiments, the invention is also directed to an electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, wherein the electrophoretic display fluid comprises a first set of particles and a second set of particles each dispersed in a transparent liquid system, the first set of particles exhibiting a color different from and contrasting to a color of the second set of particles, and wherein the first set of particles are magnetic particles while the second set of particles are non-magnetic particles, the electrophoretic display device further including an electric field application apparatus and a magnetic force application apparatus, both the electric field application apparatus and a magnetic force application apparatus being capable of being applied to each of the individual reservoirs separately.
Further, in embodiments, the invention is also directed to a method of maintaining an operation of an electrophoretic display device, the electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, and wherein the electrophoretic display fluid comprises a first set of particles and a second set of particles each dispersed in a transparent liquid system, the first set of particles exhibiting a color different from and contrasting to a color of the second set of particles and also exhibiting a different charging property from the second set of particles, the method comprising applying an electric field to an individual reservoir at risk of having particle agglomerations form therein for a period of time sufficient to prevent the formation of particle agglomerations and to break-up any particle agglomerations that may have formed.